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["John Levine" <address@concealed>]

In article <address@concealed> you write:
>You should rather fix these monitoring systems :-)

They're not broken.  It sounds like the mail setup doesn't properly
separate message submission (RFC 6409, port 587) and message relay
(RFC 5321, port 25.)

It is perfectly normal for the program that creates a message to leave
out mechanical headers like Date and Message-ID and for the initial
MTA to add them.  See section 8 of RFC 6409.

Back in the old days there was no separation and sendmail had an
unfortunate tendency to "clean up" relayed messages and mangle them.
A properly configured system separates the two and only does the
cleanup on port 587 submissions.  Any modern MTA such as postfix can
do both submission and relay.

R's,
John